I have setup such config before
Depend on What resource you have now?
You MB and CPU you use? support Vt-d?
Have another NAS for NFS/ISCSI Datastore?
My old Solaris setup like that
Zotac H55 + I5 660 + 2 x 4G RAM
1. Install ESX on usb Driver
2. Install Solaris to NFS DATASTORE (from my old nas)
3. Vt-d passthrough Intel SATA controller with 5x2T + 1SSD to Solaris VM
If you CPU and MB haven't vt-d
e.g. you have 5 x 2T + 1 SSD
create equal size Vdisk on each local harddisk
create XXG vdisk for NIL on SSD(usually same size as ram is enough)
Create XXG vdisk for cache on SSD